This invention relates generally to gas turbine engine fuel systems and, more particularly, to an improvement in systems for conveying metered quantities of powdered fuel, such as coal, to a gas turbine engine combustor maintained at an elevated pressure.
Gas turbine engines have, heretofore, been operated on solid fuels such as powdered coal. In such applications the fuel, usually stored at atmospheric pressure in a low pressure circuit of the fuel system, must be metered or otherwise transferred to a high pressure delivery circuit operative to move the fuel into the combustor against the pressure existing in the combustor. In U.S. patent application Ser. No. 184,537, filed Sept. 5, 1980 in the name of Thomas P. Kosek and assigned to the assignee of this invention, means are disclosed for metering powdered coal from low pressure storage into a stream of air flowing from an air pump into the reaction chamber of the engine's combustor. The powdered coal is entrained in the airstream and injected into the combustor for combustion. Reference may also be made to U.S. patent application Ser. No. 125,469, filed Feb. 28, 1979 in the names of Kosek and Steinhilper and assigned to the assignee of this invention, for a description of a nozzle for injecting powdered coal into the combustor. In order for the airstream to flow from the air pump to the combustor, the pressure of the stream must exceed that in the combustor. Most desirably, the airstream pressure should exceed the pressure in the combustor by an amount sufficient to effect fuel delivery but not by so much as to reduce combustion efficiency and the difference should be constant regardless of the pressure in the combustor. Accordingly, in past solid fuel delivery systems the output of the air pump has been bypassed from a point ahead of the fuel metering manifold back to the pump inlet to control delivery stream pressure. These systems are less than ideal because work must be performed to raise the pressure of the air that is eventually bypassed back to pump inlet. A gas turbine engine fuel system according to this invention represents an improvement over these and other heretofore known solid fuel delivery systems.